It is well known that dispersing agents are useful additives to cementitious materials and especially Portland cement. By more effectively dispersing the cement paste, the aggregate particles, reinforcement, fillers, pigments, or other ingredents of the final mixture are more homogeneously coated and the resulting concrete product has more compressive strength. Because the dispersing agent does not function to increase adherence as one of its prime properties, the resulting concrete with the dispersing agent alone does not generally show an improvement in internal adherence or in adherence to adjacent material; and accordingly, the flexural strength of the resulting concrete is not increased. Further, outside of some relatively minor increase in density due to the greater homogeneity, penetration or resistance to absorption of liquids is not achieved by the use of a dispersing agent alone.
Latexes are also well-known additives for use with cementitious material and Portland cement mortar mixtures. Latexes of rubbery polymers are known to provide greater continuity throughout the mixture and thus a greater adherence within the mixture as well as adherence to adjacent materials. It is thus known that the use of latex does provide an increase in the flexural strength of concrete when it is an additive to the cement mixture. It also provides greater plasticity and workability to the mixture, and a reduction in the viscosity of the mixture, permitting a reduction of the water to cement ratio. The rubber film forming latex extends throughout the cured concrete and appears to reduce the penetration and increase the resistance to absorption of liquids, especially corrosive salt solutions. This is extremely beneficial when the cement mixture is used for concrete pavements by reducing the amount of attack caused by the salts used for ice and snow prevention or removal.
U.S. Pat. No. 3,677,780 illustrates the use of a beta-naphthalenesulfonic acid-formaldehyde condensate as an additive to cement to obtain increased compressive strength. The patent teaches that the use of the additive has an even greater effect in increasing compressive strength than the mere reduction of the water cement ratio. However, there is no disclosure whatsoever of the use of a latex as an additional component to the cement mortar mixture.
U.S. Pat. No. Re. 28,722, reissued Feb. 24, 1976, discloses the use of about 5-25% based on the weight of Portland cement of a styrene-butadiene copolymer latex, and a combination of three surfactants, one anionic, one non ionic and a polyorganosiloxane.
U.S. Pat. No. 2,662,064 shows a cementitious pumpable coating composition including cement, both a fibrous filler and a non-fibrous filler, a stabilized latex, and a water soluble thickener. The requirement of a thickener causes an interference to the curing action of the cementitious material being used and would defeat the purpose of the feasibility of the present invention. The lowest amount of latex disclosed is an amount equal to the amount of dry cement, and this proportion of latex would not result in a workable concrete for the purposes of the present invention.